Motorcycle Handling

Screen shot 2016-02-01 at 6.27.21 AM

In a story on CycleWorld.com, Kevin Cameron goes into some of the notable failures in motorcycle development, specifically in the handling department, and in the process gives a pretty damned good explain of various fork and swingarm attempts and the reasoning behind them.  Here are a few examples.

The Constant Wheelbase idea:

There was a period in English motorcycling when experts announced that best handling could only result from designs having constant wheelbase. Based on this, the telescopic fork was rejected because it lets the front wheel move back as it compresses, shortening the wheelbase. The best suspension, therefore, was a leading or trailing link fork, with its travel restricted so its motion was mostly vertical.

…shot down by nothing less than Reality:

Now reality intervened in the form of the 1950 Manx Norton, with a telescopic fork up front and a swingarm at the rear.

The Chain Swingarm Pivot Thing:

Wise men now came up with one that has been rediscovered by inventors about 50 times since then, namely, to achieve perfectly constant rear chain center distance by pivoting the swingarm on the same axis as the gearbox sprocket. This looks really attractive on paper, but when you build a powerful motorcycle this way, it squats down under power in corners and pushes the front, running wide. Hmm, closer study reveals that successful designs locate the swingarm pivot higher than this, using chain tension to generate a lift force that neutralizes acceleration squat, stopping front-end push.

Seriously?  That’s truly a shocker to me…  but fair enough, and this is pretty important when you’re trying to place the motor in the frame.

Finally, the Low Center of Gravity thing:

The next doctrine was that the soul of good handling is a low center of gravity….  Then it turns out that when a motorcycle rolls over for a turn, it doesn’t roll around a line through its tire footprints. It rolls around its own center–of-mass, which is about 20 to 22 inches above ground level. That in turn means that for quickest direction-changing, large masses such as engine and fuel should be close to that height.

So, conclusions?  Well, we circle back around to, maybe Honda, Yamaha and others actually do have some vague idea of what they’re doing and a modern bike is a pretty damned good evolution of the art, maybe generations of engineers and riders have tried just about everything, and actually are able to design something better than I can in my quasi-engineering-inspired ramblings while driving long distances on empty turnpikes, and, yes, when trying to figure a layout for batteries and a motor in a frame, maybe, just maybe it’s a good idea to try to lay stuff out with the same C/G and sprocket location as the original beast.

There’s also an interesting discussion of turbocharging, and the problems – handling problems, mind you – with the application of power to the rear wheel that a turbo creates.  Now that’s interesting.  If you were to make a chart of power delivery, and put a turbo on one end, I’d guess the next stop would be a two-stroke, then a four-stroke, with an electric drivetrain at the other end.  Put that in the context of handling, and, am I drawing too much of a fine line by again stating that an electric drivetrain is a completely different animal than a gas bike at speed?

I’m sure that won’t hinder the next generation of design students building all sorts of alternative structures to hang the front and rear wheels off, however.

Johammer-Electric-Motorcycle-1

 

Advertisements

2 responses to “Motorcycle Handling

  1. Funny reading about concentric swingarm pivot and drive sprocket- a little antisquat is a good thing. Likewise on centre of gravity too. The right CoG is the one that works, not what you’re ‘supposed ‘ to use. Voltron has been a good study of the matter. Suspension guys wouls be completely baffled when doing the opposite works better 🙂

  2. I think the argument for front forks is very simplistic. I could argue that in the 90’s John Britten showed that the Hossack front was superior. As for centre of gravity the first major improvement the Norton Manx did (’54) was to change the motor design to lower the centre of gravity.

    Do I think that current chassis design is the holy grail for handling. Nope. Do I know what is, Nope. But I am pretty sure the next custom build bike I do will have a Hossack front end. It has a few significant advantages over the pre ’50’s constant wheelbase design and telescopic forks. One: lower unsprung weight. Two: wheel travel can be designed as you need it, say shorten a bit for sharper handling then stay constant. Three: easy and cheap to make.

    Watch a few videos of the Britten racing and see how much more “settled” it is under heavy braking for a corner.

Comments?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s